Halysites are another coral you may find in the region. Also known as chain corals, these rare corals form in chain-like growths, but they are not found in Devonian-age rocks. Instead, Halysites largely went extinct in the Silurian Period, just before the Devonian, and they are native to the older rocks of the southern portion of Michigan’s Upper Peninsula. They are occasionally found in the Little Traverse Bay area and other Petoskey stone-rich localities thanks to the incredible power of the glaciers of the most recent ice age.
The older Halysites chain corals tend to be more fragile than Petoskey stones, with more-delicate features that are easily weathered away. For this reason, they are scarce and highly prized by local beachgoers. Aside from being corals, they share little in common with Hexagonaria species. You may sometimes see chain corals referred to as “parasitic,” but this is a misnomer derived from their occasional presence with or upon other ancient corals.
A water-worn stone containing clear Halysites chains
Specimen courtesy of Dean Montour
This unusually fine specimen illustrates the delicate chain-like structure of Halysites. Though it was found near Petoskey, it originated much farther north.
Specimen courtesy of Dean Montour
